to succeed unexpectedly in a dire situation; to succeed despite all odds; literal meaning: 'salted fish coming back to life'
Definitions (粵典–words.hk)
語句
喺遭遇挫折或者失敗之後，意外噉突破或者成功返（注意：雖然「鹹魚」可以解屍體，但係「鹹魚翻生」唔會用嚟講死唔去、執返條命呢個意思，唔同「死過翻生」。） to have an unexpected success after an apparent failure; literally "salted fish reviving" (Note: The phrase is never used to describe close-death encounters; 死過翻生is used instead.)